Crossed-field reentrant stream tubes having an improved drift space geometry

ABSTRACT

A crossed-field reentrant stream microwave tube is disclosed. The microwave tube includes an anode structure having a slow wave microwave circuit formed therein. A circuit sever interrupts the microwave circuit to define a microwave field-free drift space in the radial gap region between the circuit sever and the cathode structure. The surface of the cathode structure which faces the circuit sever is contoured to provide a varying radial spacing between the circuit sever and the cathode over a portion of the field-free drift region to enhance debunching of the reentrant electron stream. In a preferred embodiment, the cathode is contoured to provide both increasing radial spacing in the axial direction from both ends toward the center of the field-free region and also circumferentially contoured to provide increased cathode-to-anode spacing taken in the downstream direction of the drift region to move the electron stream away from the anode circuit at downstream end of the drift space which corresponds to the input end of the microwave circuit.

United States Patent [72] Inventor Andrew S. Wilczek Old Bridge, NJ.

[21] Appl. No. 829,640

[22] Filed June 2, 1969 [45] Patented Oct. 19, 1971 [73] Assignee Varian Associates Palo Alto, Calif.

[54] CROSSED-FIELD REENTRANT STREAM TUBES HAVING AN IMPROVED DRIFT SPACE GEOMETRY 6 Claims, 4 Drawing Figs.

[52] U.S.Cl SIS/3.5,

[51] Int. Cl H0lj 25/42 [50] Field of Search ..315/3.5, 36,

[56] References Cited UNITED STATES PATENTS 3,069,594 12/1962 Feinstein 315/393 3,198,979 8/1965 Sidoti 315/393 R. E our Prir nary ExaminerHerman Karl Saalb'ach Assistant Examiner-Saxfield Chatmon, .lr. AttorneysStanley Z. Cole and Gerald L. Moore ABSTRACT: A crossed-field reentrant stream microwave tube is disclosed. The microwave tube includes an anode structure having a slow wave microwave circuit formed therein. A circuit sever interrupts the microwave circuit to define a microwave field-free drift space in the radial gap region between the circuit sever and the cathode structure. The surface of the cathode structure which faces the circuit sever is contoured to provide a varying radial spacing between the circuit sever and the cathode over a portion of the field-free drift region to enhance debunching of the reentrant electron stream. In a preferred embodiment, the cathode is contoured to provide both increasing radial spacing in the axial direction from both ends toward the center of the field-free region and also circumferentially contoured to provide increased cathode-to-anode spacing taken in the downstream direction of the drift region to move the electron stream away from the anode circuit at downstream end of the drift space which corresponds to the input end of the microwave circuit.

1 5 #3 iN m B CROSSED-FIELD REEN'IRANT STREAM TUBES HAVING AN IMPROVED DRIFT SPACE GEOMETRY DESCRIPTION OF THE PRIOR ART Heretofore, crossed-field microwave tubes have been built employing a reentrant stream and a drift space for debunching the reentrant electron stream. In such prior art tubes, the radial spacing in the drift region has been contoured by including an array of bars for the anode, similar to the bars employed in the anode circuit except that they are uncoupled from the microwave circuit, to provide a varying radial spacing in the drift region to further enhance debunching of the electron beam. However, such anode contouring has not served to move the electron stream away from the anode nor to concentrate the electron stream in the axial center of the drift space. Such prior art tubes having contoured anode surfaces in the field-free drift region, are disclosed and claimed in US. Pat. No. 3,198,979 issued Aug. 3, I965 and assigned to the same assignee as the present invention.

SUMMARY OF THE PRESENT INVENTION The principal object of the present invention is the provision of a crossed-field reentrant stream microwave tube having an improved drift space geometry.

One feature of the present invention is a contoured cathode surface facing an anode circuit sever, the contour being such as to provide a substantially increased radial spacing between the circuit sever and the cathode over a substantial length of the field-free drift region, to enhance debunching of the reentrant electron stream existing from the field-free drift region.

Another feature of the present invention is the same as the preceding feature wherein the cathode surface is contoured in the axial direction to increase the radial spacing between the circuit sever and the cathode near the axial center of the fieldfree drift region to concentrate the electron beam toward the axial center of the field-free drift region.

Another feature of the present invention is the same as any one or more of the preceding features wherein the cathode surface facing the anode sever is circumferentially contoured to provide a substantially increased radial spacing between the anode and cathode at the downstream end of the field-free drift region, as comparedto the upstream end, to move the reentrant electron stream away from the anode at the upstream end of the following microwave circuit.

Another feature of the present invention is the same as any one or more of the preceding features wherein the cathode electrode surface is contoured by a plurality of circumferentially directed steps.

BRIEF DESCRIPTION OF THE DRAWINGS Other features and advantages of the present invention will become apparent upon a perusal of the following specification taken in connection with the accompanying drawings wherein:

FIG. I is a transverse schematic line diagram of a crossedfield reentrant stream microwave amplifier incorporating features of the present invention,

FIG. 2 is an enlarged sectional view of a portion of the structure of FIG. 1 taken along line 22 in the direction of the arrows,

FIG. 3 is an enlarged sectional view of the structure of FIG. 1 taken along the line 33 in the direction of the arrows,

FIG 4 is a schematic linearized line diagram depicting the electron trajectories and the operation of the drift space geometry of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. I there is shown a crossed-field reentrant stream microwave amplifier tube 1 incorporating featurcs of the present invention. The tube 1 includes a centrally disposed, generally cylindrical, cathode electrode structure 2 concentrically surrounded by an anode electrode structure 3. The anode electrode structure 3 includes a microwave slow wave circuit 4, such as a strapped bar array, operable in a forward wave mode. The microwave circuit 4 is interrupted by a circuit sever portion-5, such as a conductive block, to define an upstream end 6 and a downstream end 7 for the microwave circuit 4, such upstream and downstream ends being disposedadjacent opposite circumferential ends of the circuit sever 5.

A crossed-field reentrant stream interaction region 8 is defined in the annular space between the cathode and anode structures 2 and 3, respectively. A magnet structure, not shown, produces an axially directed magnetic field B, directed out of the paper, within the annular interaction region 8. A; power supply 9 supplies a positive potential, as of 30 kv., to the anode 3 relative to the cathode 2. A control electrode ll, of generally sector shape having an arcuate extent of approximately 60, forms a portion of the cathode electrode structure 2 and is insulatively supported relative to the remainder of the cathode electrode 2, such that it may be pulsed to a potential intermediate the potential of the cathode and the anode. A pulser 12 is connected between the cathode and the control electrode 11 for pulsing the potential of the control electrode 11 positive relative to the remainder of the cathode for collecting the electron stream and turning off the tube upon the termination of each of the inputmicrowave pulses to be amplified.

An input coaxial line 13 is connected to the upstream end 6 of the anode circuit 4 for applying microwave energy to the circuit 4 to be amplified. An output coaxial line 14 is connected to the downstream end 7 of the microwave circuit 4 for extracting amplified microwave energy from the circuit 4 and for transmitting the output energy to a suitable utilization device, such as an antenna or load, not shown.

In operation, microwave energy is applied to the microwave circuit 4 via input coaxial line 13. The control electrode 11 and the remainder of the cathode electrode structure 2, which forms a cold cathode secondary emissive sole portion 15, is operated at the cathode potential. The input microwave energy drives certain of the electrons into the secondary emissive sole 15, to produce a secondary electron stream 2 which cumulatively interacts with the wave energy on the circuit 4 to produce an amplified output microwave signal which is extracted from the tube 1 at output coaxial line 14. The electron stream e, at the output end 7 of the microwave circuit 4, is bunched into spokes of space charge which drift through a microwave field-free drift region 16 wherein the spokes of space charge are debunched and the debunched electron stream reenters the crossed-field interaction region 8 at the upstream end 6 of the microwave circuit 4. The reentrant nature of the electron stream e provides electronic feedback for increasing the efficiency of the tube 1. Upon termination of each of the input pulses to be amplified, the control electrode 11 is pulsed positive via pulser 12 to collect the electron stream end and to turn the tube off to prevent spurious output from the tube 1 following each of the input microwave pulses to be amplified.

The surface of the cathode electrode 2, which faces the circuit sever 5, is contoured both in the axial and circumferential direction, as shown more clearly in FIGS. 2 and 3, to facilitate debunching of the electrons in the field-free drift region 16. More particularly, a plurality of circumferentially directed steps 18 are formed in the surface of the cathode 15 facing the circuit sever 5. The steps 18 serve to vary the radial spacing between the cathode surface and the opposed circuit sever 5 to produce a radially directed electric field which decreases toward the axial center plane 19 of the field-free drift region 16. The increased radial spacing decreases the electric field and causes the electrons of the stream to reduce their circumferential velocity in accordance with the reduction in the electric field intensity. As a consequence, the electrons near the axial ends of the electron stream, where the steps are closer to the sever 5, have a higher velocity than the electrons near the axial center plane 19 of the stream as, such that the spokes of space charge are smeared or debunched.

In addition, the greater radial spacing between the cathode surface and the anode sever 5, near the axial center plane 19 of the drift region 16, causes the electrons to be concentrated near the axial center plane 19. This concentration of the electron stream toward the axial center plane 19 reduces leakage of the electrons out the axial ends ends of the interaction space 8 and concentrates the electrons in the region of most intense electric field of the microwave fields on the microwave circuit 4, for enhanced interaction with the fields of the circuit 4 after passage through the field-free drift region 16.

The cathode surface facing the circuit sever 5 is also contoured in the circumferential direction such that the radial spacing between the cathode surface and the sever increases in the direction of the electron stream e. This circumferential contouring tends to pull the equipotential lines away from the anode sever 5. Since the electrons tend to follow the equipotential lines, the electron stream is pulled away from the anode circuit sever 5, as seen in FIG. 4. In addition to pulling the electrons away from the anode circuit, this circumfcrcntial contouring of the cathode surface further serves to decrease electron back bombardment of the cathode surface, such that electrons of the stream are not lost by being collected on the cathode 15. Thus, there is a conservation of the electrons in passing through the-field-free region 16. As the electron stream 2 reenters the interaction region adjacent the upstream end 6 of the microwave circuit 4, the electrons will tend'to return to the position of the equipotential line on which they entered the field-free drift region 16. However, due to the inertia of the electrons, they cannot abruptly recover this position and, as a consequence, the electron stream is moved away from the anode slow wave circuit at the upstream end 6 to facilitate the collection of the electron stream by the control electrode 11, thus, reducing the positive potential that needs to be applied to the control electrode 11 for collection of the electron stream to terminate operation of the tube. In a typical example of the circumferential contour, the radial spacing between the anode 5 and cathode 2, at the downstream end of the drift region 16, is approximately twice the corresponding radial spacing at the upstream end thereof. in addition, the height h of the steps 18 increases toward the downstream end of the field-free drift region 16. in a typical example the field-free drift region 16 occupies approximately 60 of circumferential arc.

Although the improved drift space geometry of the present invention has been described, thus far, as employed in a crossed-field reentrant stream tube of the type wherein the anode surrounds the cathode this is not a requirement and these improved drift space geometries are equally applicable to crossed-field reentrant stream tubes of the type wherein the cathode surrounds the anode. Also the slow wave circuit 4 need not be of the bar type but may take any one of a number of different basic configurations such as vane, or cavity types which may include any one ofa number of different coupling devices such as straps, helices, etc.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In a crossed-field microwave tube, means forming a cathode electrode structure, means forming an anode electrode structure generally concentrically disposed of said cathode to define a crossed-field reentrant stream interaction region in the annular unobstructed space therebetween, said anode electrode structure including a slow wave microwave circuit disposed facing said cathode to support microwave energy thereon for interaction with the reentrant stream of electrons circulating within the interaction region to amplify wave energy on said circuit, said anode structure including a circuit sever portion for interrupting said microwave circuit to define an upstream and and a downstream end of said circuit ad acent the ends of said circult sever and a mlcrowave fieldfree region in the space between said cathode electrode and said circuit sever, the improvement wherein, said cathode electrode structure has the surface thereof which faces said circuit sever contoured to provide a substantially increasing radial spacing between said circuit sever and said cathode over a substantial circumferential extent of said field-free region to enhance debunching of the reentrant electron stream exiting from said field-free drift region.

2. The apparatus according to claim 1 wherein said contoured cathode surface is contoured in the axial direction to provide a substantially increased radial spacing between said circuit sever and said cathode near the axial center plane of the field-free drift region as compared to the axial end of said drift region, whereby the electron stream is debunched and concentrated toward the axial center plane of said field-free region.

3. The apparatus according to claim 1 wherein said cathode surface is contoured in the circumferential direction to provide a substantially increased radial spacing between the circuit sever and said cathode at the downstream end of said field-free drift region as compared to such spacing at the upstream end of said drift region, whereby the circulating reentrant electron stream is moved away from said anode at the upstream end of said microwave circuit.

4. The apparatus of claim 2 wherein said cathode surface which is axially contoured is also circumferentially contoured to provide a substantially increased radial spacing between said field-free drift region than at the upstream end thereof, whereby the circulating reentrant electron stream is moved away from said anode at the upstream end of said microwave circuit.

5. The apparatus of claim 2 wherein said contoured surface of said cathode electrode comprises a plurality of circumferentially directed steps formed in said cathode surface.

6. The apparatus of claim 5 wherein the height of said steps increases toward the downstream end of said field-free drift region. 

1. In a crossed-field microwave tube, means forming a cathode electrode structure, means forming an anode electrode structure generally concentrically disposed of said cathode to define a crossed-field reentrant stream interaction region in the annular unobstructed space therebetween, said anode electrode structure including a slow wave microwave circuit disposed facing said cathode to support microwave energy thereon for interaction with the reentrant stream of electrons circulating within the interaction region to amplify wave energy on said circuit, said anode structure including a circuit sever portion for interrupting said microwave circuit to define an upstream end and a downstream end of said circuit adjacent the ends of said circuit sever and a microwave field-free region in the space between said cathode electrode and said circuit sever, the improvement wherein, said cathode electrode structure has the surface thereof which faces said circuit sever contoured to provide a substantially increasing radial spacing between said circuit sever and said cathode over a substantial circumferential extent of said field-free region to enhance debunching of the reentrant electron stream exiting from said field-free drift region.
 2. The apparatus according to claim 1 wherein said contoured cathode surface is contoured in the axial direction to provide a substantially increased radial spacing between said circuit sever and said cathode near the axial center plane of the field-free drift region as compared to the axial end of said drift region, whereby the electron stream is debunched and concentrated toward the axial center plane of said field-free region.
 3. The apparatus according to claim 1 wherein said cathode surface is contoured in the circumferential direction to provide a substantially increased radial spacing between the circuit sever and said cathode at the downstream end of said field-free drift region as compared to such spacing at the upstream end of said drift region, whereby the circulating reentrant electron stream is moved away from said anode at the upstream end of said microwave circuit.
 4. The apparatus of claim 2 wherein said cathode surface which is axially contoured is also circumferentially contoured to provide a substantially increased radial spacing between said field-free drift region than at the upstream end thereof, whereby the circulating reentrant electron stream is moved away from said anode at the upstream end of said microwave circuit.
 5. The apparatus of claim 2 wherein said contoured surface of said cathode electrode comprises a plurality of circumferentially directeD steps formed in said cathode surface.
 6. The apparatus of claim 5 wherein the height of said steps increases toward the downstream end of said field-free drift region. 